299 
(c) Radium in a state of equilibrium contained its radio- 
active products, each ejecting an equal number of 
а particles of definite speed, and therefore respon- 
sible for one of the sides of the polygon. 
He showed that experiment proved this to be the case. 
He also described the following experimental results: —(1) 
De-emanated radium only emitted о particles of range about 
83 ст. (2) A uniform layer cut off the same quantity from 
the range of all the « rays. t 
In the case of thin layers he showed that the curve should 
take the form of a series of steps, each step representing one 
radio-active change, and that this also was an experimental 
fact. Experiments with thin layers showed that:— 
(1) De-emanation removed all the steps but one, that of 
height 3:3 em. 
(2) Other three steps slowly came back into the curve, 
at about the proper rate, according to Rutherford 
and Soddy's theory of radio-active change. They 
had heights of about 4 cm., 4:5 cm., and 67 cm. 
respectively. 
(3) These three were all nearly equal in width, implying 
that the number of « particles in each stream was 
the same, as it should be. 
(4) A red heat temporarily removed the first two of 
these three steps, the third afterwards dying out. It 
therefore appeared that the third was due to the 
second radio-active product, the others being due to 
the first radio-active product and the emanation. 
(5) The а particle ionised more successfully towards the 
end of its career. 
The author also showed that in Becquerel’s photographic 
trace of the path of the а ray in a magnetic field there should 
be— on at least one side of the trace—more curvature in the part 
of the curve near the radium than in the part further away; 
and that in this way Becquerel's observations to that effect 
might be explained. The outer edge was, in fact, the locus 
of the ends of the rays, not the path of any one ray. 
It was more diflicult to determine the precise positions of 
the corners of the polygon in the case of thick layers than 
the positions of the steps in the curve of thin layers. Experi- 
ments on the former, conducted with dome-shaped ionisation 
chambers of various radii, had met with some degree of 
success. 
Mr. R. Kleeman had given valuable assistance during the 
research. 
